The present invention relates to a semiconductor laser device and an optical pickup which are basic components of a replaying/recording device for optical disks.
Recently, as means for reprlaying, recording, storing, and transferring various kinds of information in the form of documents, music, images, and the like, optical disks such as compact disks (CD), digital versatile disks (DVD), and the like, and optical disk devices for replaying and recording the optical disks are widely used.
Optical pickups, which are basic components that actually perform replay and recording of information, are demanded to be low in cost and to be thinner in association with recent expansion of optical disk markets and a widespread demand of portability of notebook personal computers, car navigation systems, portable mini disks, and the like. Further, on the market background that a demand for a single product capable of coping with a plurality of formats such as a CD, a DVD, and the like is increasing, an optical pickup having a function of coping with a plurality of media are earnestly desired in recent years.
For satisfying the above demands, semiconductor laser devices in which a semiconductor laser chip, light receiving elements, and various optical components, which are constitutional member of the optical pickups, are integrated and optical pickups using them have been proposed, and some of them have been used and produced in practice (see Japanese Patent Publication No. 3108976B, for example).
In the case where a semiconductor laser chip and light receiving elements are integrated, after a laser light emitted from the semiconductor laser chip is reflected by the surface of an optical disk device, the reflected light as a feedback light should be incident in the light receiving elements arranged around the semiconductor laser chip. For this reason, the feedback light is diffracted using a diffraction grating so as to be lead to the light receiving elements.
However, part of the feedback light is not diffracted by the diffraction grating and transmits directly to be incident on the surface of the semiconductor laser chip. An electrode made of a material having high reflectance such as gold is formed on the surface of the semiconductor laser chip, and therefore, the light incident in the semiconductor laser device is reflected by the electrode and heads towards the optical disk again.
In this way, when the light reflected by the surface of the semiconductor laser chip and returning to the disk again is induced, it interferes with the original emitted light. In consequence, a tracing error signal is offset by a tangential skew of the disk (see, for example, Japanese Patent Application Laid Open Publication No. 61-024031A corresponding to Japanese Patent No. 1886907B).
Under the circumstances, a wire for supplying a current to the semiconductor laser chip is bonded to the surface of the semiconductor laser chip in the feedback light incident region for scattering the feedback light so that the light reflected by the surface of the semiconductor laser chip is prevented from heading towards the disk again.
However, in the conventional techniques, a scattered light scattered at the part where the wire is bonded is incident in the light receiving elements as a stray light. This lowers especially the S/N ratio of output signals from the light receiving elements arranged in the vicinity of the semiconductor laser chip.
Further, because the different amounts of stray lights are incident in the light receiving elements, a focus error signal and a tracking error signal, which are detected by computing the output signals from the light receiving elements, are offset, generating an error in servo operation.
Moreover, in the actual mass production, positional displacement of a semiconductor laser chip mounted on a semiconductor substrate or positional displacement of a wire bonded on the upper face of the semiconductor laser chip causes displacement between the position where the feedback light is incident finally on the upper face of the semiconductor laser chip and the position where the wire bonding is performed, so that no stable scattering of the feedback light incident on the upper face of the semiconductor laser chip is attained.
In order to cope with a plurality of optical disk media, it is necessary to perform wire boding at a plurality of points for scattering various kinds of feedback lights corresponding to various beams having oscillation wavelengths of the disks. This involves complication in manufacturing process and increases the amount of the wiring material to be used, resulting in remarkable increase in cost.
Though it has been tried to absorb the light rather than scattering, every method of this kind requires an additional special manufacturing step, lowering yields and inviting difficulty in manufacturing a semiconductor laser device at low cost.